sábado, 21 de janeiro de 2017

O AVIÃO DO "ACIDENTE" COM TEORI - ASPECTOS TÉCNICOS

Beechcraft C90GT

The Beech King Airs owe four decades of success to having the best mix of cabin comfort, performance, excellent flying qualities and famous reliability. The new C90GT keeps the comfort and wonderful flying feel that pilots love and delivers a lot more performance. It can't catch the light jets, but it has dented their speed advantage without giving up cabin and cockpit room and comfort. The C90GT airframe is the same basic size as the original King Air with four to five passenger seats and the roomy squared-oval cabin shape. What makes it a "GT" are new Pratt & Whitney PT6 engines, and new four-blade propellers, that increase cruise speed by at least 25 knots and improve climb rates by as much as 50 percent at higher altitudes, all without shortening range on the same amount of fuel. The C90GT formula isn't magic. In fact, there are field modifications that exchange the original for more powerful engines on existing King Airs. But the GT is a new airplane, not just new engines. The PT6A-135A engines on the GT are rated at 550 shaft horsepower just like the Dash 21 engines they replace. But the new Pratts are really 750-shp engines that have been restricted to the lower maximum output for takeoff. That means as the GT climbs, the new engines can keep putting out full-rated horsepower to a much higher altitude. The earlier King Air 90s hit max speed at about 16,000 feet, but the C90GT hits its stride at 25,000 feet, or higher.

I got to fly the first C90GT and the climb performance was unlike a regular King Air 90. It was the prototype and lacked a complete interior, but our takeoff weight was just 600 pounds under maximum with full fuel and some other equipment onboard. Immediately after takeoff the C90GT climbed steadily at 2,200 fpm and held near that rate up to 15,000 feet, and then maintained an 1,800 to 2,000 fpm climb through 18,000 feet. We were still going up at 1,500 fpm when I leveled at 25,000 feet just 15 minutes after takeoff, with that time including a brief leveloff. That's an easy seven or more minutes less time to climb than the previous model.

Level at 25,000 feet, the C90GT accelerated until the indicated airspeed hit the Vmo limit of 186 knots, and that translated into 270 knots true airspeed. Total fuel flow was around 440 pounds per hour. That's a solid 25 knots faster than the earlier C90B at its best altitude, and 40 or more knots faster at 25,000 feet. Fuel flow was higher at that level, but the speed was so much greater that useful range is the same because flight time is reduced.

The C90GT is certified to 30,000 feet, and with the new engines can quickly climb to that level and cruise at nearly 260 knots, but I don't think many pilots will use that flight level often. One reason is that with five psi maximum cabin pressure, the cabin altitude is near 12,500 feet when flying at 30,000 feet. That's legal, but not comfortable for every pilot. Also, there is the issue of reduced vertical separation minimum (RVSM) requirements to fly above 28,000 feet. The King Air can meet the requirements, but it's an extra hassle for not much return in fuel efficiency. The cockpit of the GT is noticeably quieter thanks to props that turn a maximum of 1900 rpm compared to 2100 rpm before. The cabin on the 90 series King Airs has always been remarkably quiet and comfortable, but the cockpit is quite close to the prop tips and therefore not as quiet. The lower prop rpm really helps up front.

But the reduced maximum propeller rpm would have added to takeoff runway requirements if Beech had not made some operational changes. Though the new propellers and operating rpm are very efficient at climb and cruise, they cannot match the static thrust of the high rpm props for takeoff. So, for the first time a C90 King Air uses flaps for takeoff. With the first notch of flaps down, the new C90GT uses the same amount of runway for a sea level takeoff as the C90B. At higher elevation airports, particularly on hot days, the GT uses many hundreds of feet less for takeoff because of the new derated engines ability to continue to deliver maximum power under hot or high takeoff conditions.

Automatic propeller feathering has been available on the C90 King Airs, but was an option and not part of the airplane's required equipment as it is on the larger King Airs. For the C90GT autofeather is now standard, as is rudder bias. If an engine quits on or shortly after takeoff, the autofeather system automatically brings the dead engine propeller to feather and the rudder bias steps on the opposite rudder to keep the airplane flying straight. The rudder bias system uses bleed air pressure from the operating engine to push the rudder in the proper direction. It's a very simple system with no electronics or complicated parts. You will need to add a little foot pressure to the pedal on the good engine side yourself, but in those critical seconds after an engine failure, the C90GT with rudder bias and autofeather takes care of itself while the pilot concentrates on airspeed control. I am lucky to have the chance to fly many business jets of all sizes, and whenever I get back into a King Air cockpit I'm always pleasantly surprised by the room, particularly the headroom. King Air's have more cockpit headroom than all light jets, and even many of medium size. Pilots on the tall side will really appreciate the headroom, but pilots of any size can find a seating position that gives good visibility over the nose and to the sides. I'm 6 feet 2 inches tall, and I raise the seat in the King Air from its lowest setting, something I never do in the light jets, or even some medium-sized ones.

You won't confuse the C90GT cockpit with any brand new design turbine airplane because this King Air still has toggle switches, gauges for various systems, and only basic electronic flight instruments. But there is no denying the big airplane feel of the C90GT. The windshields are heated electrically instead of with engine bleed air and there are wipers to clear rain. The control wheels and power levers have a confidence inspiring heftiness. And you sit up high looking down on lesser airplanes, including many jets.

Passengers appreciate this same sense of size and sturdiness when they climb the airstair. There is room for a private potty in the rear of the cabin, and baggage space is internal so your stuff can be reached in flight. Beech has upgraded the C90GT cabin furnishings, including using the chairs from the top of the line King Air 350. Beech experimented with a recommended propeller 1700-rpm cruise setting, which did quiet the cockpit a little. However, when the sound level was "mapped" inside the passenger cabin, the level was higher at 1700 rpm because the noise damping had been designed to be most effective at 1900 rpm.

The logical question many ask about the C90GT is, why not buy a jet? The Cessna Citation Mustang is priced about the same, or maybe a little less, than the King Air, and is expected to have a top cruise speed almost 70 knots faster and a ceiling 11,000 feet higher. The answer for many owner-pilots is that the King Air's attraction is that it is not a jet.

The new light jets will have a cruise speed advantage on the C90GT, but it will be measured in just a few minutes over trips of several hundred miles. And if the little jets are held down low below their optimum altitudes-as is likely in congested parts of the country-the turboprop will save money at the fuel pump.

The King Air 90 family has an excellent safety record while being flown by owner-pilots. It is a logical step up from a piston twin with essentially nothing new for a pilot to learn in basic airplane handling. Pilots can have confidence in their ability to fly the GT, and more importantly, insurance companies understand the risks. The new crop of light jets has the potential to be very safe, but the industry has little experience with large numbers of single-pilot owner flown jets so there will be an abundance of caution by all.

The C90GT is already a hit with annual sales more than double the previous model, and orders are accelerating. It's an old-fashioned airplane in many ways, but gains in performance without sacrificing any of its proven qualities. As has happened so many times in the life of the King Air, it's time to take another look.